Optical, structural, and electrical characteristics of high dielectric constant zirconium oxide thin films deposited by spray pyrolysis

The spray pyrolysis technique was used to obtain high dielectric constant zirconium oxide films. These films were deposited on silicon substrates, and quartz slides from two different solution concentrations (0.033 and 0.066 M) of zirconium acetylacetonate dissolved in N,N-dimethylformamide at substrate temperatures in the range of 400–600 °C. The films are transparent with a surface roughness lower than 40 Å and with the $ZrO2$ stoichiometry. The refractive index of the films was up to 2.12 at 630 nm. Infrared spectroscopy measurements show a dominant absorption band associated to $ZrO2$ at 420 cm⁻¹ and the presence of silicon oxide $(SiO2)$ peaks as well. Cross-section transmission electron microscopy (TEM) images of these films reveal the existence of a thin layer at the silicon substrate interface with the deposited $ZrO2$ film. It is also found from both cross-section and plan-view TEM observations that the deposited layers consist of tetragonal $ZrO2$ nano-crystallites embedded in an amorphous zirconium oxide matrix. Spectroscopic ellipsometry measurements were fitted assuming the existence of a thin interface layer on top of the Si substrate, composed of $SiO2,$ $ZrO2,$ and crystalline silicon. The as-deposited films have a dielectric constant in the range from 10.9 to 17.5 when they are deposited at different substrate temperatures for the two spraying solution concentrations studied. The films withstand electric fields up to 3 MV/cm, without observing destructive dielectric breakdown.